A fuel cell using polyelectrolyte allows a hydrogen-containing fuel gas and an oxygen-containing oxidant gas, such as air, to electrochemically react with each other, such that electric power and heat are generated at the same time. The fuel cell is basically structured with a polymer electrolyte membrane that selectively transports hydrogen ions, and paired electrodes formed on both the surfaces of polymer electrolyte membrane, i.e., the anode and the cathode, respectively. These electrodes each have a catalyst layer whose principal component is carbon powder bearing platinum metal catalyst and which is formed on the front surface of the polymer electrolyte membrane, and a gas diffusion layer which has combined features of air permeability and electronic conductivity and which is disposed on the outer surface of the catalyst layer. Such an assembly made up of the polymer electrolyte membrane and the electrodes (including the gas diffusion layers) being integrally joined and assembled is referred to as an electrolyte membrane electrode assembly (hereinafter referred to as the “MEA”).
Further, on the opposite sides of the MEA, electrically conductive separators for mechanically clamping the MEA to fix the same, and for establishing electrical connection in series between the MEA and adjacent MEA, are disposed, respectively. In each separator, at the portion to be brought into contact with the MEA, gas flow channels for supplying corresponding electrodes with the fuel gas or a reactant gas such as the oxidant gas, and for carrying away the generated water or excess gas are formed. Though the gas flow channels can be provided separately from the separators, what is generally employed is to form grooves on the front surfaces of the separators to serve as the gas flow channels. It is to be noted that, such a structure body in which the MEA is clamped between the paired separators is referred to as the “unit cell module”.
Supply of the reactant gas to the gas flow channels formed between the separators and the MEA and discharge of the reactant gas and the generated water from the gas flow channels are each carried out in the following manner: through holes called manifold holes are provided at the edge portion of at least one of the paired separators, to establish communication between the inlet/outlet port of each of the gas flow channels and each of the manifold holes, and the reactant gas is distributed to the gas flow channels from the manifold holes.
Further, in order to prevent external leakage of the fuel gas or the oxidant gas supplied to the gas flow channels, or to prevent mixture of the gases of two types, gas sealing members or gaskets are disposed as sealing members between the paired separators, at the places where the electrodes are formed in the MEA, that is, so as to surround the external circumference of the power generation areas. The gas sealing members or the gaskets also seal the circumference of each of the manifold holes.
Since the fuel cell generates heat while driving, the cell must be cooled by coolant or the like, in order to maintain the cell at an excellent temperature state. Normally, a cooling portion for allowing the coolant to flow is provided every one to three cells. The general structure of a stacked battery (fuel cell stack) is as follows: the MEA, the separators, and the cooling portions are alternately stacked by ten to two hundred cells; thereafter, an end plate is disposed at each of the end portions of the whole cells with a current collector and an insulating plate interposed between the endplate and the end portion thereof, such that the whole cells are clamped between such paired end plates and fixed from both the ends through the use of fastening bolts (rods) or the like. As to the fastening method, the general method is to fasten with fastening bolts which are inserted into through holes formed at the edge portions of the separators; or to fasten up the entire stacked battery with a metal belt, having the end plates interposed therebetween.
With the stacked battery employing such a fastening method, it is important to fasten and seal the unit cell module with a fastening force which is uniform in a plane (i.e., within a plane perpendicular to the stacked direction). Recently, in order to ensure safety, a double seal capable of surely separating the combustible gas and the outside air is demanded. However, for the purpose of reducing the costs, a reduction both in the size and space of the stack is also demanded. Meeting the demand for the double seal generally invites an increase in the fastening load, complication in the fastening members, and an increase in the volume of the stack. Therefore, the demand for the double seal and the demand for a reduction both in the size of the stack and in the fastening force are conflicting.
In connection with such a fuel cell-use seal, as shown in FIG. 8, what is devised by Patent Document 1 is a carbon member as one example, which has a gasket provided with two lips 200 in parallel to each other, to thereby secure the sealing performance without inviting an increase in the surface pressure, taking into consideration of a reduction in thickness of the sealing portion, an improvement in assemblability, prevention of misalignment, a reduction in surface pressure, and excellent evenness in surface pressure.
Further, Patent Document 2 proposes a gasket 201 having a two-stepped structure which is shown in FIG. 9, as one example of a gasket capable of satisfying the requirement for a reduction in the reaction force, preventing the lip from collapsing, and maintaining the sealing performance even with slight unevenness or steps on the counter face. The gasket 201 is attached through integral molding to one of two members opposing to each other. A sealing lip 202 integrally molded to the gasket 201 to be brought into close contact with the other member is in a shape having a small collapsed volume for achieving a reduction in the reaction force.
Patent Document 3 discloses a fuel cell-use gasket including a sealing portion having an internal seal formed with a lip having a substantially triangular cross section projecting toward both sides, and an external seal positioned externally to the internal seal and formed with a lip having substantially triangular cross section projecting toward both sides, in which the internal seal and the external seal are coupled with an annular coupling portion. With such a structure, it achieves an excellent sealing performance and a suppressed reaction force, and solves the problem of the gasket being collapsed.
Patent Document 4 discloses a sealing portion provided with a sealing lip having a bidirectional sealing performance, in which a sealing lip possessing a unidirectional sealing performance is provided on one side or on both the sides of the sealing lip. Such a structure is capable of satisfying the requirement for a reduction in the reaction force, maintaining the sealing function even upon an occurrence of a collapsing phenomenon at the lip, and further, maintaining the sealing function even with slight unevenness or steps on the counter face.
Patent Document 5 discloses paired interval restricting portions, each having a cross section of a rectangular shape or the like and disposed around the periphery of a rubber sheet, in which a lip line portion having a cross section of a bell-shape or a triangular shape is disposed between the paired interval restricting portions. The paired interval restricting portions is to control the dimension such that the desired behavior of compression deformation is attained by the lip line portion.
Patent Document 6 discloses a flat seal structure with a bead-like sealing lip (also referred to as a bead) in which a rubber as a gasket body that is made of a rubber-like elastic material and that has a sealing lip portion is formed to have a triangular or bell-shaped cross section. Further, Patent Document 6 also discloses a gasket body on each of both the sides of an electrolyte membrane, the gasket body being provided with bead-like sealing lip portions two-pieces each. This makes it possible to prevent a reduction in the surface pressure peak value of the gasket body, even in a case where the bonding position of resin films on both the sides are somewhat displaced sideways.